KR890004939B1 - Semiconductive composite - Google Patents

Abstract

A semiconductive material (I) comprises an ethylen-vinyl acetate (chloride) copolymer, carbon black, silicon cpd. and an inhibitor for crosslinking between interfaces. (I) adheres to a crosslinked polyethylene substrate, or can be peeled from the substrate. Pref. the inhibitor is phenol, guinone, thiazole or thiuram sulfide.

Description

Semiconducting Composition

The present invention relates to semiconducting compositions based on ethylene-vinyl acetate copolymers or their chloride products, characterized by having adhesion to crosslinked polyolefin substrates and strippability from the substrates.

Pickled conductors, i.e. wires and cables, designed for medium to high voltage use are generally metal core conductors coaxially arranged around the core conductor, internal semi-conductive layers, crossover It consists of a combined polyolefin insulating layer, an outer semiconducting layer, a metal shield layer and an outer protective sheath. Typically the outer semiconducting layer is based on a composition containing ethylene-ethyl acrylate copolymer or ethylene-vinyl acetate copolymer and carbon black. In order to crosslink the external semiconducting layer, an organic peroxide is added to the composition.

It is important to peel the external semiconducting layer from the insulator layer in order to splic the wires and cables quickly and well. It has been proposed to chemically modify the polymer in the composition and / or to add various additives to it in order to produce a composition having adequate adhesion with strippability. For example, the adhesion between the cross-linked polyolefin insulating layer and the semiconducting layer may be based on the comonomer content, ie the ethylene-ethyl acrylate copolymer or ethylene-vinyl acetate copolymer used to formulate the composition to be used as the semiconducting layer. It is known that the weight can be reduced by increasing the content of ethyl acrylate or vinyl acetate. It is also known that the desired degree of exfoliation can be achieved by chlorinating the ethylene copolymer rather than increasing the monomer content.

It is also known that in the additive, the peelability of the semiconducting layer from the crosslinked polyolefin insulating layer can be improved by adding a silicone oil such as dimethyl polysiloxane of liquid to the composition of the semiconducting layer.

However, these methods did not prove particularly effective. Compositions containing ethylene chloride copolymers exhibit inferior mechanical properties and lower thermal stability when used as an external semiconducting layer of power cables. In addition, silicone oils are not fully suitable for ethylene copolymers and will bleed out of the composition over time when used in an amount sufficient to improve peelability, typically in excess of 5% by weight. In addition, the addition of silicone oil in an amount sufficient to improve peelability lowers the mechanical properties, in particular the elongation, of the resulting composition.

Peeling of external semiconducting layers from cross-linked polyolefin insulating layers has become a more important problem in recent extrusion techniques. According to the state of the art, insulated conductors are extruded simultaneously in three layers, i.e., the inner semiconducting layer, the cross-linked polyolefin insulation layer and the outer semiconducting layer using a coaxial extruder and then cured in a single operation. It is prepared by coextrusion. In some respects, this manufacturing method is advantageous in that this insulated conductor is formed by tight bonding of three layers and eliminates the formation of voids and partial peeling between layers caused by bending or heating in normal use. This method prevents corona deterioration and other insulation degradation. On the other hand, in such a manufacturing method, there is a problem of peelability due to the high bond strength between these layers caused by the formation of crosslinks between the cross-linked polyolefin insulating layer and the outer semiconducting layer.

As mentioned above, it is also important that the external semiconducting layer is adhered to the insulator layer, but it is also important that it can be peeled relatively easily in a short time. To cut or overlap the cable, for example, the outer semiconducting layer must be removed from the insulator layer at a distance from the end of the cable.

The present invention provides a semiconducting composition that is useful as a semiconducting layer bonded to a crosslinked polyolefin insulating layer of wires and cables since it has a controlled degree of peeling. The semiconducting layer extruded from the composition of the present invention has a suitable adhesion to the cross-linked polyolefin insulating layer of the insulator, and has a controlled peeling property such that the semiconducting layer is peeled from the insulator layer when it is to be installed, repaired or overlapped. Have

The compositions of the present invention contain ethylene-vinyl acetate copolymers or chloride products thereof, carbon blacks, silicone compounds and interface crosslink inhibitors such as phenols, quinones, thiazoles or thiuram sulfides.

The ethylene-vinyl acetate copolymer used herein has a melt index of 1 to 50 g / 10 minutes (as measured by ASTM test method D-1238) and a copolymer containing 15 to 30% by weight of vinyl acetate. Means. Suitable ethylene chloride-vinyl acetate copolymers are copolymers having a melt index and vinyl acetate content as described above and containing between 30 and 40% by weight of chlorine.

Carbon blacks which may be added to the composition of the present invention to impart semiconductivity to the composition of the present invention include furnace black, acetylene black, channel black, ketjen black and the like. Highly conductive blacks, such as Ketjenblack EC, are preferred and require smaller amounts to make the composition semiconducting.

Silicone compounds as used herein include silicone oils, silicone rubbers and silicone block copolymers that are liquid at room temperature.

Suitable silicone oils include any commercial silicone oil, in particular silicone oils of polysiloxanes having a viscosity of 6 to 100,000 centipoise at a temperature of 25 ° C.

The silicone rubber used in the present invention contains, among other components, filled or unfilled unvulcanized rubbery siloxanes having a molecular weight of 30,000 to 150,000, preferably 30,000 to 50,000.

Suitable silicone block copolymers contain the following repeating units.

R is a monovalent hydrocarbon group or oxysubstituted hydrocarbon group having 2 to 30 carbon atoms, preferably 2 to 18 carbon atoms, and m + n is 2 or more. Generally m is an integer from 1 to 100 and n is an integer from 3 to 200.

Alkyl groups such as, for example, ethyl, n-propyl, isopropyl, n-butyl, etc. of the group R; Aryl groups such as phenyl and benzyl; There exists an alkoxy group represented by residues, such as polyethylene glycol and polypropylene glycol.

Specific silicone block copolymers include poly (stearyl methyl-dimethylsiloxane) block copolymers, poly (alkylene glycol methyl-dimethylsiloxane) block copolymers, poly (phenyl methyl-dimethylsiloxane) block copolymers, and the like.

Examples of interfacial crosslinking inhibitors used in the composition of the present invention include 2,2'-methylene-bis (4-methyl-6-tert-butylphenol), 2, -di-tert-butyl-4-methylphenol Phenols such as 4,4'-thio-bis- (6-tert-butyl-2-methylphenol) and tert-butyl catechol; Quinones such as hydroquinone and 2,5-di-tert-butylhydro quinone; Thiazoles such as 2-mercapto-benzothiazole, 2, 2'-dithio-bis-benzothiazole and N-cyclohexyl-benzothiazole-sulfenamide; And thiuram sulfides such as tetramethyl thiuram disulfide.

The composition of the present invention is prepared by using these materials in the following amounts based on 100 parts by weight of ethylene-vinyl acetate copolymer or ethylene-vinyl acetate copolymer.

Carbon Black: An amount sufficient to impart semiconductivity to the composition, generally from 40 to 100 parts by weight. This amount can be reduced to 5 to 50 parts by weight in the case of highly conductive carbon black having a large surface area such as Ketjenblack EC.

Silicone compound: Usually 0.3 to 5 parts by weight, preferably 0.3 to 2.5 parts by weight.

Interfacial crosslinking inhibitor: usually 0.01 to 1.5 parts by weight. In this range, a sufficient effect is not obtained, and out of this range, outflow occurs over time after molding.

The semiconductive composition of the present invention may be crosslinked by organic peroxides such as di-α-cumyl peroxide, 2, 5-dimethyl-2, 5-di- (tert-butyl-peroxy) hexin-3 and the like. (See, US Pat. Nos. 3,954,907 and 4,017,852).

The semiconducting composition of the present invention may contain other conventional additives such as anti-aging agents, processing aids, stabilizers, antioxidants, crosslinking accelerators, fillers, pigments, etc., in amounts known in the art, as needed.

Mixtures of the above-mentioned materials may also be used as necessary.

The semiconducting composition of the present invention is prepared by mixing the materials in the following amounts:

Formulation weight part

Ethylene-Vinyl Acetate Copolymer

Or ethylene-vinyl acetate copolymer 100

Carbon black 65

Polymerized 2, 2, 4-trimethyl-1, 2-

Dihydroquinoline (Antioxidant) 0.8

Lead Stearate 1

Di-α-cumyl peroxide ^* 1

＊ Unless otherwise stated

The addition of silicone compound and interfacial crosslinking inhibitor to this base composition is as described in the table.

The composition is press molded under the following conditions to produce a sheet of 150 mm x 180 mm x 0.5 mm thickness.

Pressure: 85㎏ / ㎠

Temperature: 120 ℃

Molding cycle time: 10 minutes

In addition, a 150 mm x 180 mm x 2.0 mm thick sheet is molded as described above from a composition consisting of polyethylene, 0.2% by weight of antioxidant and 2% by weight of di-α-cumyl peroxide.

The sheet formed from the semiconducting composition based on the ethylene-vinyl acetate copolymer is placed on the sheet formed from the polyethylene composition, and the sheets are laminated together using a compression molding machine under the following conditions to prepare a laminate.

Pressure: 20㎏ / ㎠

Temperature: 180 ℃

Molding cycle time: 15 minutes

A 100 mm x 120 mm specimen is removed from the laminated sheet and tested for peelability on a tensile tester. The two layers of each specimen are separated at 23 ° C. at a rate of 500 mm / min, with the semiconducting layer at an angle of 90 ° to the polyethylene layer. The force required to separate these two layers is called "stripping strength" and is expressed in kg / 10 mm.

Data for the inventive compositions are described in Table I and data for “controls” are described in Table II.

As used herein for a composition, "having adhesiveness and peelability" means that a force of 0.3 kg / 10 mm or more is required to remove the semiconducting layer from the insulating layer. Semiconducting layers that require a peel force below this limit are likely to separate from the insulating layer when bent in use of the cable, thus reducing the insulation.

The abbreviations and symbols used in Tables I and II have the following meanings:

EVA: Ethylene-vinyl acetate copolymer containing 6 g / 10 min of melt index and 28% by weight of vinyl acetate.

1-EVA: Ethylene chloride-vinyl acetate copolymer containing 25% by weight of chlorine, prepared by chlorinating EVA.

Silicone-Compound A: Silicone block copolymer having the following repeating units:

Wherein R is a C ₂₂ alkyl group.

Silicone-Compound B: Silicone block copolymer having the following repeating units:

In which R is a residue of polypropylene glycol.

Interfacial Crosslinking Inhibitor X: 2, 2'-methylene-bis (4-methyl-6-t-butylphenol)

Interfacial Crosslinking Inhibitor Y: 2-mercapto-benzothiazole

Interfacial Crosslinking Inhibitor Z: 4, 4'-thiobis (6-t-butyl-2-methylphenol)

"Broken" in the Penetration Strength column means that the specimen ruptures before it separates.

The marks "i" and "s" in the crosslinking column indicate that the specimen is insoluble (i) and soluble (s) in hot toluene at 90 ° C, respectively.

Silicone rubber: Unvulcanized silicone rubber 201 (manufactured by Toshiba silicon Co., Ltd.)

Silicone oil: NUC silicone oil L-45, viscosity 2000 centipoise (manufactured by Nippon Unicar Co., Ltd.)

The data in the table indicate that satisfactory peelability was not obtained when the silicone compound was used alone. This is true even if 3 parts by weight of the silicone compound is used based on 100 parts by weight of the polymer, regardless of the form of the silicone compound. When the amount of the silicone compound is used in an amount of 5 parts by weight or more, it becomes difficult to mix in preparing the composition or the mechanical properties of the resulting composition are worse.

Peelability is still poor even at a concentration of 1.5 parts by weight when the interfacial crosslinking inhibitor is used alone, and an outflow occurs at this concentration.

This drawback is eliminated when a mixture of silicone compounds and crosslinking inhibitors are used. Mixing these two components also reduces the amount added.

As a result of the synergistic effect when the silicone compound and the crosslinking inhibitor are used in combination, the peelability can be improved by a smaller amount of the additive. This synergistic effect not only lowers the cost of the semiconducting composition but also results in unexpected results: no additives spill onto the surface of the composition, improved moldability, and improved surface smoothness. , Reducing stains on dies and dies, and improving mechanical properties such as tensile strength and elongation.

TABLE I- (Example)

Table II (Control)

Remarks: (1): It is difficult to mix the composition.

(2): The composition is impossible to mix.

Note: ＊: No crosslinking agent

＊＊: Specimen cannot be manufactured

↑: not measuring data

Claims (14)

A semiconducting composition comprising an ethylene-vinyl acetate copolymer or an ethylene-vinyl acetate copolymer, carbon black, a silicone compound and an interfacial crosslinking inhibitor, and which can adhere to the crosslinked polyethylene substrate and can be peeled off from the substrate. The semiconducting composition of claim 1, wherein the interfacial crosslinking inhibitor is selected from the group consisting of phenol, quinone, thiazole, and thiuram sulfide. The method of claim 1, wherein the ethylene-vinyl acetate copolymer or ethylene chloride-vinyl acetate copolymer; About 40 to about 100 parts by weight of carbon black; About 0.3 to about 5 parts by weight of a silicone compound; And about 0.1 to about 1.5 parts by weight of an interfacial crosslinking inhibitor selected from the group consisting of phenol, quinone, thiazole, and thiuram disulfide. The composition of claim 3 wherein the ethylene-vinyl acetate copolymer contains about 3 to about 40 weight percent chlorine. The composition of claim 3 wherein the interfacial crosslinking inhibitor is phenol. 6. The composition of claim 5 wherein the phenol is 2, 2'-methylene-bis (4-methyl-6-tert-butylphenol). 6. The composition of claim 5 wherein the phenol is 4, 4'-thio-bis- (6-tert-butyl-2-methylphenol). The composition of claim 3 wherein the interfacial crosslinking inhibitor is thiazole. The composition of claim 8 wherein the thiazole is 2-mercapto-benzothiazole. The composition of claim 3 wherein the silicone compound contains repeating units of the general formula:

Wherein R is a C ₂₂ alkyl group. The composition of claim 3 wherein the silicone compound contains repeating units of the general formula:

Wherein R is the residue of polypropylene glycol. The composition of claim 3, further comprising an organic peroxide. A conductor having on the conductor a composition according to claim 3 or a crosslinking product thereof as a semiconducting layer. 4. The composition of claim 3 wherein the silicone compound is silicone oil, silicone rubber or silicone copolymer and is present in an amount of 0.3 to 2.5 parts by weight.